1. Field of the Invention
This invention relates to a female engaging member of a surface fastener made of a thermoplastic synthetic resin material and comprising a flat plate-like substrate and a large number of pile-shaped engaging elements arranged on the surface of the substrate as well as to a method of manufacturing such a female engaging member. More particularly, the present invention relates to a female engaging member of a surface fastener adapted to be manufactured efficiently and continuously in a single step and showing excellent engagement strength and peeling strength relative to a mating male engaging member, both the substrate and the pile-shaped engaging elements being adapted to be made of an appropriate material suitable for the application and selected out of a variety of different materials. Male engaging elements realized in a mushroom-shaped or hook-shaped form or in some other form may be arranged on the front or rear surface of the substrate. The present invention also provides a method of manufacturing such a female engaging member.
2. Prior Art
Generally, a known surface fastener comprises a male engaging member having a flat plate-like substrate and a large number of anchor-shaped or mushroom-shaped male engaging elements arranged on the substrate and a female engaging member also having a flat plate-like substrate and a large number of pile-shaped female engaging elements arranged on the substrate so that they may be brought into mutual engagement over the entire surface thereof when their substrates are placed oppositely and pressed against relative to each other and the engaged male and female members may be separated from each other when they are pulled from each other. Therefore, a surface fastener is generally used as an article composed of members having two structures. Alternatively, male and female engaging elements may be arranged on a same side or on the opposite sides of one flat plate-like substrate.
Male engaging elements having various different profiles such as hook-shaped, mushroom-shaped or palm tree-shaped are currently used. The male engaging elements of a surface fastener are typically produced by preparing a sheet of knit or woven fabric that contains a large number of looped monofilaments and then cutting the looped monofilaments of the fabric. Alternatively, the male engaging elements of a surface fastener may be prepared integrally with the flat plate-like substrate by introducing a molten resin material onto a die wheel having a large number of engaging-elements-forming cavities on the peripheral surface thereof, while rotating the die wheel in one direction.
On the other hand, female engaging elements are typically realized in the form of densely arranged piles of fibers. Thus, a female engaging member is generally produced by preparing a sheet of knit, woven or non-woven fabric or synthetic resin as substrate thereof that carries a large number of piles of fibers on the surface. The piles of fibers are normally produced at the time of knitting or weaving the fibrous flat plate-like substrate as integral part of thereof. U.S. Pat. No. 5,512,234 discloses a method of forming piles on the surface of a flat plate-like substrate made of a sheet of synthetic resin by preparing a sheet of synthetic resin integrally with male engaging elements while introducing a sheet including a large number of long fibrous filaments arranged in parallel onto the peripheral surface of a heated drum having a large number of loop forming cavities to form loops arranged zig-zag and then combining it with the synthetic resin sheet so that a part of each of the loops made of the long fibrous filaments are fixed integrally to the surface of the synthetic resin sheet by fusing.
Japanese Patent Application Laid-Open No. 63-63405 also discloses a method in which the surface of a sheet of thermoplastic synthetic resin is softened and a sheet of knit or unwoven fabric carrying a large number of piles on the surface is pressed against and firmly attached to the thermoplastic synthetic resin sheet. Then, the softened material of the synthetic resin sheet permeates into the rear surface of the sheet of fabric and becomes integral part thereof to stabilize the profiles of the piles so that the obtained product does not require any back coat.
Finally, Japanese Patent Application Laid-Open No. 2-191735 discloses a method of forming a female engaging member comprising steps of feeding multifilaments of two different types having different melting points into a preliminary air twisting apparatus with different feed rates, producing a covered thread being heat-set by covering a core thread with a large number of looped fibers, arranging a plurality of such covered threads in parallel on a sheet of unwoven fabric and heat treating them at temperature higher than the melting point of the low melting point mutilfilaments but lower than that of the high melting point multifilaments to fuse the low melting point multifilaments to be integral with the surface of the sheet.
However, with the method of manufacturing a female engaging member disclosed in U.S. Pat. No. 5,512,234, it is difficult to bend the large number of multifilaments to be formed evenly and arranged zig-zag uniformly unless the tension applied to them when they are fed in parallel onto the drum is controlled highly accurately, and a plurality of operating members of the apparatus for forming the female engaging member have to be driven synchronously and quite accurately in order to firmly attach the filaments, maintaining the loops in shape onto the surface of the synthetic resin sheet. Thus, the manufacturing cost will be high and only limited types of products can be manufactured because the drum is costly and requires cumbersome operations for replacement so that the proposed method has limited applications.
A female engaging member as disclosed in Japanese Patent Application Laid-Open No. 63-63405 carries a thermoplastic resin sheet on the entire rear surface of the fabric instead of a back coat material, and a part of the material of the sheet permeates the sheet of fabric to get to the entire rear surface and becomes integral part thereof. Thus, the female engaging member is accompanied by a drawback of not being sufficiently soft and flexible because of the existence of the thermoplastic resin sheet and the rigidity that appears on the interface.
A female engaging member as disclosed in Japanese Patent Application Laid-Open No. 2-191735 is prepared by causing substantially untwisted multifilaments of two different types having different melting points to be "preliminarily twisted" by means of a whirling air flow, where the multifilaments arranged in parallel are made to pass through the whirling air flow and become intertwined randomly, heat setting them and thereafter melting the low melting point multifilaments at temperature between the two melting points of the multifilaments so that they are fused integrally with the substrate sheet (cover). Thus, a part of the low melting point multifilaments are fused to be integral with the substrate sheet and, since they are intertwined with the high melting point multifilaments randomly and become liquefied as being molten, the molten resin can easily be agglomerated at the crossings of high melting point multifilaments to bond the latter each other at the crossings.
As a result, however , the loops of the high melting point multifilaments that have been produced are reduced in size to make the female engaging elements on the female engaging member less apt to be engaged with male engaging elements and some of the female engaging elements may become totally unfunctional. If the function of the engaging elements is to be secured when the molten resin are agglomerated at the crossings of high melting point multifilaments, various parameters for producing the multifilaments of two different types to cross have to be controlled rigorously to involve difficulties in maintenance.
In view of the above identified problems, it is therefore the object of the present invention to provide a female engaging member of a surface fastener carrying engaging elements having a novel profile in which the engaging strength and the peeling resistance can be readily set, and which can be manufactured continuously by a relatively simple process without requiring serious maintenance efforts, and thus the engaging member has high productivity, and the manufacturing method of the engaging member.